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Isaf forces are training their Afghan counterparts ahead of a full handover in 2014

A Nato soldier in eastern Afghanistan has been shot dead by three men in Afghan police uniform, officials say.

The men fled the area after Sunday's attack, Nato's International Security Assistance Force (Isaf) says.

It says the incident is now under investigation.

There have been a growing number of cases where Afghan soldiers have killed Nato colleagues. More than 20 foreign troops have been killed in "rogue shootings" this year.

Observers say this has eroded morale among foreign forces.

Isaf provided no further details about Sunday's attack and did not specify the nationality of the dead soldier.

However, a police source said the attack took place in Kandahar province, according to the AFP news agency.

Members of the Nato-led Isaf force are training their Afghan counterparts in preparation for a full handover of responsibility for security by 2014.

Revelations in February that US troops burned copies of the Koran at a base in Afghanistan - reportedly by accident - as well as the shooting of 16 Afghans by a US soldier in March have inflamed public opinion against the foreign forces.